The goal of this observational study is to learn about the potential differences in morbidity of thyroidectomy (removal of the thyroid gland) depending on the preoperative hormonal status. The main question it aims to answer is: Do patients undergoing thyroidectomy for thyreotoxicosis (thyroid hyperfunction) due to Graves' disease or Amiodarone induced thyreotoxicosis have comparable complication rates depending on their thyroid metabolic status prior or during the procedure. The data from participants undergoing a thyroidectomy at one of the study sites will be prospectively registered in the EUROCRINE registry, including an add-on module for additional study specific routine data. The operation itself, the preoperative or postoperative treatments are not altered in any way.